Fix a performance regression when deleting large amounts of text

Having the event manager in focus during deletion causes text removal to
be approximately 3x slower.
Merge pull request #309 from peitschie/perf-regression

Fix a performance regression when deleting large amounts of text
Suppress fail messages for expected-to-fail tests

Having these always log out regardless makes it very difficult to pin
point failing tests.
Fix incorrect test expectations (reproducing issue 261)
Implemented faster & more robust cursor position fixing logic

Existing behaviour was slow if the cursor has a large distance between the
anchor and focus nodes. It also tended to lose the first letter when right
near the start of a paragraph or root boundary.

New logic avoids the need for expensive positional lookups, instead
exploiting the fact that the actual step value of the cursor is expected
to be unmoved. This allows the start and end points of the range to be
simply moved to their nearest valid step.

* Re-ordered ambiguous elements in test "Remove_DeleteLastCharacterInSpan"

Fixes issue #261